1. Field of the Invention
The present invention relates to an automotive vibration isolating device comprising vibration isolating rubber members which are provided as a pair on left and right sides of an automotive vehicle.
2. Description of the Related Art
Conventionally, it is known that suspension arms of left and right suspensions of an automotive vehicle are supported on the body of the automotive vehicle via rubber bushings which are vibration isolating rubber members. In addition, known as such a rubber bushing is a rubber bushing of a sealed, fluid-filled type in which two or more fluid chambers are formed in a rubber element which communicate with each other via orifice portions, whereby viscous resistance generated when filled and sealed fluid flows between said fluid chambers via the orifice portions provides a damping action of vibrations. Note that the same specification is used for rubber bushings used on the left and right suspensions of the automotive vehicle.
When an automotive vehicle is running on the surface of a road from which the automotive vehicle picks up pulse-like inputs (or a road having joints in the surface thereof), a longitudinal vibration force is transmitted from the road surface to the vehicle body via the left and right suspensions of the vehicle. This vibration force is a resultant force from vibrations deprived from longitudinal resonance of unspring members caused by the resiliency of rubber bushings whose masses are unsprung loads (hereinafter, referred to as bushing resonance) and vibrations deprived from longitudinal oscillations of the suspensions caused by resonance in directions of torsion of the tires (hereinafter referred to as tire torsion resonance) FIG. 6 shows a power spectrum of the longitudinal vibration force transmitted to the vehicle body, and in the graph, a portion designated by reference character xe2x80x9caxe2x80x9d whose frequency is around 19 Hz is deprived from the bushing resonance, while a portion designated by reference character xe2x80x9cbxe2x80x9d whose frequency is around 45 Hz is deprived from the tire torsion resonance.
Here, in order to reduce the longitudinal vibration force that is transmitted to the vehicle body, it is considered to set low the spring constant of the rubber bushings, but this results in the deterioration of steering stability such as the bad response of the vehicle body when steered, and the countermeasure is not practical.
The present invention was made in view of the above situations, and an object thereof is to provide an automotive vibration isolating device for effectively reducing vibration that is transmitted to the body of an automotive vehicle.
With a view to solving the problem, according to the invention, there is provided an automotive vibration isolating device, including a pair of vibration isolating rubber members provided on left and right sides of an automotive vehicle and having a difference in dynamic characteristics between one and the other of said vibration isolating rubber members. Here, in a case where the vibration isolating rubber members are of a sealed, fluid-filled type, there is provided a difference in dynamic characteristics, which are vibration damping characteristics provided by fluid filled and sealed in the vibration isolating rubber members, between the one and the other of the pair of left and right vibration isolating rubber members. Preferably, a vibration frequency ratio between the and the other of the pair of left and right vibration isolating rubber members in which the rubber members provide maximum damping is 1.5 or more.
According to the invention, there is caused a difference in phase between the vibration transmitted via the one of the pair of left and right vibration isolating rubber member and the vibration transmitted via the other of the same, whereby the vibration transmitted via the one vibration isolating rubber member and the vibration transmitted via the other vibration isolating rubber member cancel each other, the vibration force that is transmitted to the vehicle body being thereby reduced effectively.